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Can your intestines be sucked out by a commercial aircraft's toilet?
Say for example you have a complete seal (unlikely) between yourself and the toilet. Is the amount of suction possible to pull one's intestines (or insides) out and into the toilet? I think (probably a joke) on a NASA show that the toilets in space can do that, but probably just meant jokily. But, back to the original question, is it possible?

Travel.SE has a dupe of this

Obviously not. Every day, probably millions of people use plane toilets and this has never happened. If it did, airlines would get sued into oblivion.

this question is quite... gross.

Well, while kind of an odd question, there does happen to be a pretty simple answer so...
The Mythbusters proved, in one of their episodes, that the pressure differential created by an airline toilet seat isn't even enough to make a person be stuck to the seat itself.
I think it's fairly common knowledge (or can at least be assumed) that if you wanted to suck someones guts out of their body you would, as a first step, need to be able to create a proper vacuum seal between that person and the toilet seat.  Since it's impossible to create a proper vacuum seal with an airline toilet, we can deduce that that self same toilet lacks the power to suck out your organs.
So, if you were worried, don't be.  Feel free to use that airline throne all you want ;).


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Why is on-time performance important for commercial flights?
From the perspective of an airline, is it just to avoid penalty and also to portray reliable service to the customers?  Or is it just a matter of logistics and scheduling?

Hi Tobias, welcome to aviation.SE. I have to admit that I do not see your question well suited for the scope of this site. Please wait also for the opinions of other users, but it might be better for you to ask on travel.SE.

Who wants to fly an airline that never gets you where you need to be on time? Especially if "where you need to be" is a connection for an airline that knows how to keep a schedule...

@Federico - It used to be that airline operations (from an operations standpoint, not a customer standpoint) where considered in scope.  This seems to fit into that, buuuuuut, do we still count those sorts of questions as in scope?  If not, then I would agree with you.

@JayCarr I see the point. I retract the VTC, but I hope that the answers will not focus on the passenger side of things.

I am new here. So, I should ask my question at the other site but not this?

@Tobias I think you are fine so long as this questions is about how airlines operate from the perspective of the airline (why do airlines pick particular planes?  Are some airports better for certain jets than others? Etc).  If its a question of how they operate from a passenger perspective (ie., how good are the seats?  how does this rewards program work? etc), then it's better on Travel.SE.  Right now your question is a little ambiguous which it is, perhaps if you edited it a bit...

@Tobias I edited your question to better reflect what I feel is the "spirit" of your question.  If I am incorrect, please feel free to revert the edits.  Apologies if I assumed too much :)

Perhaps the question should be rewrote as "how important [...]" or "what are the main reasons for [...]".

I can think of a few:

Any delay in the flight is a waste of valuable resources- the flight, cabin and ground crew who have to be paid and the aircraft itself, which is not generating any revenue but costing money for the airline. Also, the airline may have to pay for the time the aircraft spends in the airport.
There is an economic cost associated with on-time performance- for example, passengers are more likely to take airlines which have better on-time performance over others.
Another case is that of customers taking connecting flights- again, on-time performance could be the difference here. This means loss of business for the lower performing airline.
For airlines operating multiple trips per day, the delay and the associated costs are cumulative; for example, if the first flight of the day is delayed, it snowballs into the day- requires replanning for the rest of the day in other airports and causes further delays.

For the airline industry, the delays cost billions of dollars every year (1 and 2) and can reduce the operating revenues by a few percentage points (3). The table below, taken from the NEXTOR report on Total Delay Impact Study shows the cost to US airlines due to delays.

As can be seen, the the costs due to delay to airlines are quite high.

source: Stack Exchange

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Why does an aircraft leave a white smoke trail?
Why does an aircraft leave a white smoke trail?

Good thing you put that arrow there. I would have totally missed the smoke

At least this wasn't a "chemtrail" question!

needs a freehand circle...

https://pbs.twimg.com/media/Bve2BCdIcAAELAn.png

Actually, there are three types of trails an aircraft can leave in the sky:
1. Condensation of water vapor in the exhaust gas and/or the wake
This needs the very cold, very dry air at higher altitudes between 6000m and 12000m. Water vapor in the exhaust stream condenses and, pushing the local air above its saturation water content, forms a white, frozen mist. Also, particles from partially burnt fuel form condensation cores wich stabilise the contrail and let it grow over time from humidity already present in the air. Depending on the atmospheric humidity, these contrails disappear rather quickly by sublimation or can stay in place for hours and even grow into cirrus clouds. They are called condensation trails or short "contrails".

Cirrus clouds triggered by aircraft contrails (picture source)
While the added water vapor in the exhaust gas helps in contrail production, the condensation happening in the pressure field around an aircraft can already produce a contrail all by itself. If the relative humidity is close to saturation and the condensed droplets freeze quickly, the aerodynamic contrail will disappear rather slowly. The same condensation happens also at lower altitude but will not leave a contrail  in temperatures above 0°C. Fog (liquid droplets) will vaporize quickly, but when frozen the condensation will last longer, until the water is re-absorbed by the air by sublimation, a much slower process than evaporation.

Engine and aerodynamic contrail forming behind an A340 (picture source)
2. Smoke from unburnt or partially burnt fuel
This was prevalent in early jets and allowed to spot them from a distance - just follow the black line, at its tip is an aircraft. Smokeless combustor cans which allow more fuel-air mixing put an end to this. For more information I recommend the excellent web page contrailscience

This B-47 uses rockets to accelerate quickly which leave the biggest smoke trail, but also the old J-47 left a lot of smoke behind (picture source).
3. Oil mist or smoke flares
The third source is shown in your picture: Oil is injected into the hot exhaust stream which forms a dense mist. This can be done with jets and piston engines, and gliders or parachutists use smoke flares. Once they are ignited (in most cases electrically) they burn down and cannot be switched off.

Smoke flares on the wingtips and fuselage of a glider (picture source)
There are many more things that can be sprayed from an aircraft (fuel, obviously, when it has to be dumped in an emergency, fertilizer or insecticides, silver iodide to seed clouds), but these are special cases. I encourage you to visit contrailscience.com for an exhaustive list of those other cases.

LS-10 glider dumping ballast water (picture source)

One more comes to mind, crop dusters.

The B-47 also used water injection to increase take-off performance. Injecting water cools the engine and gives more mass to accelerate out the back but, because the temperature is lower, there's a lot of partially burnt fuel coming out as black smoke.

Also note that many gliders can carry around a couple hundred litres of water ballast, that is typically dumped before landing, which also leaves a faint, white trail.

Probably worth noting that, in the third case of oil/smoke flares, these are unique in that they are deliberately generated for show/display purposes (often with added colours, etc) or to attract attention to the aircraft, while for the rest they are merely a byproduct of the aircraft's normal operation.

@J..., Indeed. The Blue Angels during a performance are obviously going to have a different set of concerns than a commercial jet is!

Most aircraft that leave trails aren't leaving smoke.  It's condensed water vapour; essentially, clouds. These are called contrails. This can be caused by the water in the engine exhaust condensing, or by the disruption of the air by the passage of the aircraft triggering the condensation of water that was already present.

Some aerobatic aircraft have smoke generators which leave much thicker and more visible trails which can be turned on and off and don't depend on particular atmospheric conditions.  White is most common but other colours are possible.

The Blue Angels in your photo are an example of aerobatic aircraft with smoke generators.

Well, condensation trails are (a kind of) smoke. Because white smoke (e.g. from wood fire or from cars when it's cold) is always condensing water vapour that is one of the combustion products.

The Blue Angels and other display teams have smoke generators in their jets, which have the specific purpose of generating a smoke trail because it looks cool. Smoke trails at airshows are generally for that purpose. The generators inject a small amount of diesel into the jet exhaust to generate white smoke, and dyed diesel to make coloured smoke.

So the smoke is special effects, interesting, thank you

@Tom "Smoke On" is something of a tag-line even for the Red Bull Air Race

Since it isn't burned, why don't they use #2 heating oil instead and save taxes?

You may also see 'smoke' coming from the wingtips or other parts of fighter aircraft under high G loads. This is actually water vapor condensation from the extremely low air pressure that is briefly generated by a hard turning fighter, and it disappears quickly.

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How do high-wing and low-wing aircraft compare in terms of structural damage in a crash?
Which type of aircraft is more likely to avoid damage to the aircraft structure: high-winged aircraft or low-winged aircraft?
What factors influence the type of damage usually sustained during a crash?

By crashworthy do you mean avoiding damage to crew and cargo, or avoiding damage to the aircraft?

Related: What are the pros and cons of high-wing compared to low-wing design?.

"What factors decide aircraft crashworthiness" I think you should explain that to us first.

By crashworthiness I mean avoiding damage to aircraft structure .

A design can not avoid damage: it can be designed to minimize the impact of being struck, however, reinforcement would be at the cost of weight.

Regardless of wing position, a crash will damage most or all of the aircraft structure. Since low wings have dihedral, mild cases like a wheels-up landing will mainly affect the center fuselage rsp. the wing box. But most crashes occur in an odd orientation of the aircraft towards the ground, so at least one wing and the fuselage will suffer damage.
There are a few designs which will tolerate foreseeable abuse. On the Su-27, two long iron bars run along the lower fuselage and are the first to contact the ground in absence of wheels. After such a landing, the aircraft is simply jacked up and put into service again.

Su-27 on the ground after belly landing (picture source). Just look at the paint job – the abuse this aircraft suffered is not restricted to this unorthodox landing style.
The main gear of the A-10 only partially retracts, so the bottoms of the wheels stick out of the gear bays and will contact the ground first. A belly landing with an A-10 will require a bit of repair but normally the aircraft is back in the air within a week.

A-10 on the ground after belly landing (picture source). The landing gear design is on purpose: It limits damage in a belly landing. Few aircraft have been designed with such foresight.
Similarly, for tail strike testing a bumper structure is added at the lower rear fuselage. In absence of such precautions, lengthy workshop stays are unavoidable.
But most crashes are less benign. The main factor in a crash is the relative velocity between the aircraft and the structure it crashes against. In most cases, this is a sizeable portion of flight speed, so the energies involved are immense (mass times velocity squared, divided by two).

Boeing 737 Crash site (picture source). As can be seen, both wings and fuselage are heavily damaged. The wing location was not a factor in the extent of the damage. That is how a real crash looks like. Unfortunately.

Even in a relatively "benign" crash, it gets bad real quick. Consider the debris field or Asiana 214, a B777 which crashed by executing pretty much a normal landing, just somewhat short of the runway. Despite the damage, there were only three fatalities, two of which were determined to not have been wearing their seatbelts during the landing.

Unfortunately, weight saving efforts in aircraft design render them "not very crashworthy", a bit like comparing an aluminum can (aircraft) to a steel one (car).
The high wing offers a slight advantage in that it (very importantly) gives greater latitude of control just prior to crash by enabling a higher degree of freedom in roll angle without catching a wing tip.  This is especially critical in a water ditching (see sea plane design).
So you want your "crash" to be as much like a normal landing as possible.
While a low wing may offer the advantage of absorbing more energy while the crash is in progress, catching a wing tip and "cartwheeling" is disasterous and will result in a rapid disintegration of the aircraft and non-survivable forces on its occupants in many cases.

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What is this light passenger prop airplane which crash landed in East Kalimantan, Borneo in 1983?
Plane crash landed in Borneo jungle in 1983.

That registration looks like PK-DCR to me. It's a little bit blurry, but especially if you zoom in, it's fairly readable.
A quick web search for that registration and "airplane" brings me Wikipedia's page on Deraya Air Taxi, which indicates that

On November 1982, Indonesian Aerospace 212-100 PK-DCR of Deraya Air Taxi and PT Pupuk Kaltim was damaged when it approaching Bontang. No fatalities in this accident.

The 212-100 brings us to the CASA C-212 Aviocar.
Looking at the pictures on Wikipedia, it's pretty close, so that's probably it. Note the pretty distinctive tail section, and the relative dimensions:

(source; photo by RuthAS, published under CC-BY-3.0)

(source; photo by John Wheatley, published under under GFDL-1.2)

Believe these were assembled locally in Indonesia by IPTN.

Thanks for walking through your search process instead of just providing an answer. If you teach a man to fish...

@FreeMan That was my idea as well. Knowing where to start, answering the question itself was pretty trivial, but hopefully showing how to approach (no pun intended) questions like this will help at least some other people as well, who are curious about aircraft in other pictures. The real key here was that the registration was visible, so I didn't have to do much guessing.

The aircraft was a CASA 212 registered PK-DCR which crashed on November 8th 1982, near Bontang, East Kalimantan
Bureau of Aircraft Accidents

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Instrument Currency Scenarios
I am currently trying to understand 61.57 and it’s instrument currency requirements for pilots. I have made some 2 scenarios here, and it would be great if I could get some feedback to my questions.
Scenario #1
In this one, I have completed 6 instrument approaches and one hold in March. By counting back, I am current until the end of August 31. My question is how many approaches do I have to do in September to regain my currency if I am trying to act as PIC during IFR in that month?
Scenario #2
This is where I get a little confused. Say I did 5 approaches and one hold. Because I didn’t do a 6th approach, when am I not current? Also what is the staring date of my “6 month grace period?” And alternately, if I did not do anything during the grace period, what is the date when I must do and IPC check?

First off are these approaches done either in actual or simulated IMC?

Your scenarios are a little confusing.  In scenario #1, you say that you did six approaches in March, but you only show two on your paper.  In order to answer your question, we will need to know the exact dates of all six approaches which made you current as of March.  Similarly, in scenario #2, if we are to assume that you are starting out current, we need to know all of the approaches which made you current in the first place in order to determine when your currency lapses.

related: Is there a maximal time to pass a type rating?

To answer question #1 (assuming you are flying an airplane):
§61.57 (c)(1) states that:

Use of an airplane, powered-lift, helicopter, or airship for
  maintaining instrument experience. Within the 6 calendar months
  preceding the month of the flight, that person performed and logged at
  least the following tasks and iterations in an airplane, powered-lift,
  helicopter, or airship, as appropriate, for the instrument rating
  privileges to be maintained in actual weather conditions, or under
  simulated conditions using a view-limiting device that involves having
  performed the following—
(i) Six instrument approaches.
(ii) Holding procedures and tasks.
(iii) Intercepting and tracking courses through the use of
  navigational electronic systems.

As of Sept 1, to maintain instrument proficiency, you will be required to accomplish items i-iii in either an airplane under actual or simulated IMC (you must have at least passed the FAF and begun the final segment of the approach under these conditions for it to count) or have accomplished this in an approved simulator or FTD appropriate to the category and class of aircraft you seek currency in.  See §61.57 (c)(2).  Therefore in Sept, you would be required to accomplish at least 1 IAP in order to remain instrument proficient for that month.  It is suggested at this point to accomplish the required 6 approaches, hold procedures and course tracking in Sept to avoid repeating this process often while still maintaining instrument currency, though this is not required to meed minimum instrument proficiency standards.
Question #2:  see first paragraph of §61.57 (c)(1) - you must have accomplished tasks i-iii within 6 months of any IFR flight where you are acting as PIC.  In scenario #2 you are never current as you have not accomplished tasks i-iii within 6 calendar months for any month shown.  Assuming that you were instrument current in December of the previous year (items i-iii accomplished within that month), you still have a "grace period" to fly the approaches with a safety pilot starting in July of this year.  If items i-iii of §61.57 (c)(1) are not accomplished by December of this year, an IPC will be required as of January 1 of next year to maintain instrument proficiency.
Item iii of §61.57 (c)(1) is a little bit of a contention, but if you are not flying contact or precision radar approaches only to maintain instrument proficiency, you will have used navigational electronic systems to fly these instrument approaches or fly the holding patterns with so item iii can be counted towards with the accomplishment of items i and ii.


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How long before a Medivac should the pilots be ready?
If you are on home reserve how long is it required that the operator notify you of a flight before required Take off time?
Is there a regulation or documentation to support this or is it operators discretion

Welcome to aviation.SE! If you're asking about regulations, please always tell us which country you're interested in.

Medivac pilots (at least the ones in my city) are at the hanger/pad 24/7.
My home field (KPNE) happens to be where some of the medical choppers are stored and dispatched from. In Philadelphia they tend to not be stored at the hospitals. I have met some of the pilots and one of the crew nurses. Where I am the facility is staffed 24/7 much like a road ambulance facility so that as soon as a call comes in they are ready to fly. The helicopters them selves are kept in a hanger, always fueled and alway ready to fly, on these neat rolling carts so that a tug can pull them out as the pilots are getting things squared away in the cockpit.
One of the hospitals in the suburbs keeps their chopper at the hospital (which is fairly close to KDYL) and is avalible 24/7 as well.
I also happen to over look one of the 4 hospital helipads in the city from my home. The pad is generally kept open for arrivals and on a decent weather day that can mean upwards of 10 landings (I have no idea what they are transporting).
I had the pleasure of meeting one of the guys that helped design the Philadelphia Class B. The airspace is specifically designed so that all of the hospitals sit under shelves such that the helicopters can come and go without needing a bravo clearance to expedite their travel times.

Its worth mentioning that ready to fly and will fly are not the same thing and the latter is at the operators discretion. Ultimately the pilots make the go no-go decision and if the weather is dicy rescue teams generally will not fly.

If you’re talking about a life flight operation such as one based at a hospital, the pilots have duty hours where they remain in close proximity with the helicopter and can respond immediately to a call if it comes in.
Response is ultimately up to the pilot in command aboard the helicopter.  The flight crew is never told the nature of the emergency to prevent it from influencing their decision to depart, particularly in bad weather.  So a call to evacuate someone from an automobile accident receives the same priority as one to say transport a low urgency patient to a hospital for surgery.

The crews not being told is an intriguing one - that's definitely not the case in the UK and seems a little short sighted. Is that across the whole of the USA?

Do you have a source on them not being told? I have heard that before as well but still haven't found where it might say that or even if the general public would have access to that information.

https://www.telegraph.co.uk/news/health/8508956/Londons-Air-Ambulance-saviour-of-the-skies.html is a source about the London Air Ambulance not telling its drivers, but they don't specify if the policy also extends to the pilots.

The reason for doing so is to prevent the urgency of the patients needs from influencing the risk management decisions of the crew, possibly leading to dangerous situations like this https://youtu.be/51njl0n_dvI

@user1937198 LOL.. the 'Telegraph' is NOT a source of anything...


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Can you fly the plane manually without disengaging autopilot?
Let's say you are engaged a Boeing 777 with autopilot on and you bank or pitch. Will the plane respond?.
If so. will the plane try to return to its parameters once you quit handling the controls?.
Same question for any Airbus.
I read that in the case of a TCAS RA you need to disengage the autopilot and fly manually. But let's suppose your TCAS tells you to Climb and you pull your yoke without disengaging the AP. What would happen on a Boeing or on an Airbus?

The autopilot on a modern airliner isn't a single system. Rather, it's a combination of systems which work together to control the plane.
I'm not particularly familiar with the 777 specifically, but in general, the autopilot of a modern airliner will be able to do four main different things:

Keep the wings level
Maintain or change altitude
Maintain or change course
Adjust engine power

These can also be used via the Flight Management Computer to fly a preprogrammed course at designated altitudes by way of a set of specified waypoints.
For example, if the plane is flying at a heading of 180°, and the pilot turns the heading knob to change this to 200°, the autopilot will make a turn to the right to come to the new heading. In order to maintain altitude during the turn, it will need to adjust engine power and/or pitch, because the bank to turn costs energy which ultimate must come from the engines.
However, it's possible for the pilot to disengage, say, the autothrottle, while leaving the rest of the autopilot turned on. If so, the pilot will be handling the engine power levers, while the autopilot might be controlling, say, the speed during a climb or descent so as to ensure that the airframe isn't overstressed. If the pilot then also pulls or pushes the stick or yoke, the altitude maintenance system might also disconnect, but the autopilot can still help the pilot stay on course. And so on.
Generally, the autopilot will disengage one axis of control when the pilot manipulates the controls that control that axis.
For example, if the pilot turns the yoke or pushes the sidestick to the side in order to bank into a turn, the autopilot will likely disengage the wings leveller, possibly after a delay where the pilot's inputs are considered a temporary override, but it might still very well be controlling the altitude and engine power. This provides a quick autopilot override; if you get a TCAS RA saying climb, you just pull the yoke or stick back, which overrides or disengages the part of the autopilot that maintains altitude, while still leaving the automatic course and engine power control active. Since the autopilot controls the throttle at that point, the pilot doesn't need to worry (much) about the speed dropping too far and getting close to a stall during the climb. (Correspondingly, if the RA was for a descent, the pilot wouldn't need to worry about overspeeding the plane.)

Most autopilots on conventional cable operated control systems use an electric servo that drives the cable run via a capstan (basically an electric bi-directional winch with its own little cable loop linked into the main cable run).  There is one for the elevator and one for the ailerons (most modern autopilots are only 2-axis; the rudder is automatically operated by the yaw damper system which is a separate system).
There are two clutches between the motor drive and the capstan, a toothed on-off clutch and an always-engaged friction slip clutch.  The tooth clutch is engaged/disengaged by the A/P.  The friction clutch is there to allow the A/P servo to be overpowered by manually applied force if the tooth clutch doesn't disengage.
There are torque sensors in the servo drive system that sense the force the servo is working against and tell the A/P computer.  If you apply control input without disengaging the A/P, the A/P will initially resist your input but if you apply enough force you will break out the slip clutch to overpower the servo and move the control.  After a short delay the A/P computer will sense the unusually high sustained torque being applied as the servo struggles against your own input (it can't win because of the slip clutch), and kick the A/P off.
On a TCAS RA you don't have to go that far because in addition to several other disconnect triggers in the cockpit, there will be an A/P disconnect button on the control wheel near your flying-hand thumb someplace.  If you get a TCAS RA, you immediately jab the AP disconnect to kick it off as soon as you grab the column.  This is something you train for in the sim during initial and recurrent training.

The autopilot will always disengage when you try to override the controls. Manual control has priority over autopilot.
For the Boeing 737, the control mode changes to CWS (Control wheel Steering), which is an autopilot mode but follows control column inputs. So if you manually set it on 12 degrees pitch down (please do not do this in real life) then the autopilot will keep it there.


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Why are test crashes not made harder on the airframe?
This is one of the videos of the crash: 727 Test Crash. It seems it was more of a hard landing without gears. Why wouldn't the experimenters have made it more of a really hard crash if they needed to study the effects of a crash on a plane? Would slamming down the plane really hard (maybe even nose down) given a more realistic scenario and more valuable data rather than making it soft?

"Everyone definitely dies, can we have another $50M for the next test?"

They aren't MythBusters, going for the biggest boom possible.   They wanted to study a situation that was borderline survivable, and try to improve the survivability of it.

They already know the results of a hard crash.  They were interested in improving the outcomes for people in "softer" crashes.

Not at all.  I love their big booms.   Its just not applicable to aviation research.

Reducing an airplane and its contents to pieces no larger than a pack of cigarettes may rank high on the "KEWL!" scale, but it ranks remarkably low on the "We learned something useful" scale. Put another way, the size of the fireball is inversely proportional to the amount of information gained.

If the plane crashes with high vertical speed, the decelerations involved are so insanely huge that there is absolutely no way to make it survivable. That is well explained in
Even after years of research, why are planes unable to keep passengers alive in case of a fiery crash?.
However in many cases the aircraft is still, at least partially, controllable, so a crash-landing can be made. And that is the case where survivability can be improved by careful design, so that is the case they were testing.
This is also relevant for accidents on landing where the aircraft simply does not have that much vertical speed. Together these scenarios cover more accident cases than the out of control scenario.

It makes sense that the biggest benefit in terms of lives saved per dollar spent would be taking a crash that was in a barely unsurvivable state to a barely survivable state. If I made a list of scenarios to gather data on, that would be at the top!

The Sioux City crash is a good example of a "softer" crash where increasing survivability would be a good idea.

Well, theoretically, if everyone had an ejection seat...

More people would die by failure/wrong activation of the seat than by actual crashes. And planes would have half the capacity and tickets would be several-fold more expensive.

@MartinArgerami perhaps that's it - decrease aviation-related deaths by pricing most people out of the market!

@Agent_L: I was joking :)

@Mehrdad worst joke ever

Even if the ejection seat was correctly deployed, people without proper training can not cope with the forces involved in an ejection

Because they wanted to analyse survivability, making the crash non survivable would have defeated the point.

Would slamming down the plane really hard (maybe even nose down) given a more realistic scenario and more valuable data rather than making it soft?

Gone, everything is gone then. What are you going to try to improve from the outcome of such a test? Forget the real airplanes I have never been able to salvage a model aircraft that crashed nose down for any reason whatsoever.
I have on many times crash landed a model safely that had its landing gear malfunction and that's the practice that gives you valuable lessons for future landings. If you had an airplane without a landing gear and you wanted to study how can you improve chances of its survivability you would want to make a survivable attempt in the first place. You wouldn't want to crash it hard deliberately and then try to pick up pieces of the landing gear to find out what could you have done better.

The basic principle of the airworthiness regulations is risk analysis. If you can demonstrate that a particular scenario has a sufficiently low risk of ever happening, you don't need to consider the consequences if it does happen. As an order of magnitude, "sufficiently low risk" means you might expect something to happen at most once during the full lifetime of all the aircraft of that type - which may be a period of 50 years or more for a popular aircraft type where thousands of aircraft were manufactured.
Landing a partly controllable aircraft with the gear up is more likely to happen than that "extremely rare" probability, so you need to demonstrate what the consequences are, hence the test. But there are thousands of possible but extremely unlikely scenarios that could (and most likely would) lead to the loss of the aircraft. For those scenarios, you design to reduce the risk of the event happening at all, not to deal with the consequences if it does happen.
A topical example: you don't try to design planes that will survive explosions in mid flight. Rather, you try to design systems to ensure that planes don't carry explosive material in the first place.

Actually, luggage containers do try to take explosive contents into account.  It is also wise to take explosive engine failure into account.

But this test had nothing to do with airworthiness regulations.

authors: Bob Jarvis - Слава Україні


text:
When is an aircraft handed over from Center to Approach?
I'm trying to understand how an IFR flight an ACC (center) controller communicates the hand over to the pilot to contact local airport frequencies.
I tried listening LiveAtc but my English is not so good and I still have a couple of questions. I must emulate a center hand over to local destination frequencies, is this order correct for pickup the right frequency?
Approach (if present)
Departure (if present)
Tower
Is departure eligible if an approach frequency is not available?
If approach is available, which ATC gives landing clearances, tower or approach?
Also at which distance from airport ACC should do the hand off to the approach frequency?

Is this for a "virtual artcc" or some other simulation activity?

Yes I'm working on a free ATC plugin for X-Plane

Why not go for real controllers in x-plane? VATSIM e.g.

A lot of people simply is not ready for VATSIM or IVAO, or can't follows whole flight from start to the end, and for this reason, could run in troubles with communities. Virtual ATC is still an high requested feature in flight simulation, especially for newbies.

In general, aircraft are handed over on frequency to the next controller via a simple instruction to change the frequency:

R: "Lufthansa One Two Tree, contact Langen Radar 128.550"
  A: "Contact 128.550, Lufthansa One Two Tree"

The simplified order of contacted stations for a commercial flight, depending on availability and airspace structure is:

Delivery (if available)
Apron/Ground (if available)
Tower
Departure (if available, sometimes handled by Approach)
Enroute ACC/Center (multiple stations along the route)
Arrival/Approach
Director (if available / in use)
Tower
Ground (if available)

The point and altitude or flightlevel where the handoff is initiated is agreed upon in Letters of Agreement between the different sectors or ACC/ARTCC stations.

(Source: SentryRaven - Own Work)
The above picture shows the airspace around Köln/Bonn (EDDK) Airport, with the Köln Arrival East (KAE) sector being actively displayed in black. The STAR entry / clearance limit fixes are GULKO and KOPAG, in the east. Most traffic not arriving via NOR VOR in the west will terminate at these two fixes, which also serve as the handoff fix between the center controller (Paderborn High, Taunus and/or Rhein Radar Upper Control) and the arrival controller responsible for Köln East Sector. The Letter of Agreement between those sectors states that traffic arriving to Köln/Bonn via GULKO and KOPAG is to be cleared to FL100 and cleared for the respective STAR out of GULKO or KOPAG. The handoff is initiated approaching FL100 and approaching the entry fix, before the sector boundary.
The handoff is therefore based on airspace structure and sector boundaries, not on a preset distance from the airport. While arrivals from the east are handed off at FL100 over GULKO and KOPAG, arrivals from the west at NOR VOR are handed off at FL140-FL170.

Landing and Take-Off clearances are issued by the Tower controller, as the approach controller is not necessarily based at the same airport but in most cases in a remote facility together with other approach and center controllers. They have no visibility of the airport and can thus not issue these clearances.
The handoff to Tower usually happens when the aircraft is established on the final approach segment of the published approach (usually after passing the Final Approach Fix (FAF)) or a visual approach to the runway.
The phraseology is the same as above:

R: "Germanwings Two Six Alpha, contact Tower 124.975"
  A: "124.975, Germanwings Two Six Alpha"

I also should tell that I'm trying to simulate this behavior in a flight simulator, I should simplify the way to implement it, and I guess the best way to do it is to choose an average distance for the last ACC communication and hand-over to approach. Should be 20-30 nautical miles from airport, a realistic distance for trig this call? I understand it is incorrect, but unfortunately simulation requires approximation.

@ntnll You can base the calculation on the following rule of thumb: TMA airspaces  range up to FL100 or FL245, sometimes something in between. There is no general rule, but each country and each airport is differently. For each 10.000ft of descent, you need to calculate 30 NM. So a handoff from Center to Approach at FL200 would be 60-70 NM from the airport. A handoff at FL100 would be at 30-40 NM.

thank you very much, I can't vote yet, but I accepted the answer, thanks you very much, for now I'll use rough calculation you suggest. In the future I'll try to implement some most efficient calculations


text:
Did Concorde's sonic booms affect other air traffic?
Given that Concorde's sonic boom reached the ground, it also must have reached other nearby air traffic.
How was this dealt with? I imagine passengers would not welcome hearing a loud boom during their flight.

http://acousticstoday.org/wp-content/uploads/2015/06/Concorde-Booms-and-the-Mysterious-East-Coast-Noises-Peter-H-Rogers-and-Domenic-J.-Maglieri.pdf

This doesn't answer your question as written, but it is worth noting that due to the high take-off and landing speeds required by that wing, they had to have much wider separation of traffic around Concorde flights than for Heavies.  It would generate strong vortex winds.

Good point. Obviously there'd be a natural separation during the flight as well, since Concorde was significantly higher than any other traffic.

According to this airliners.net post (written when the Concorde was still flying, BTW), the Concorde's sonic booms could often be heard from other aircraft, but never posed problems for said other aircraft:

Sometimes, to the South of Ireland, during the early part of the acceleration on a Westbound flight, Concorde flies over subsonic traffic that is arriving from the USA and cruising around FL370-FL410. If close to this traffic, by which I mean 10-15 miles, then ATC will often warn them that they may be "boomed" as the shock waves pass over them.
From the reports I've heard from some of these crew, this can vary from nothing to a clearly audible double boom, but nothing to cause any concern or alarm.


text:
Why is it 'aileron right and elevator up' with a front-right wind in a tailwheel airplane?
Question: How should the flight controls be held while taxiing a tailwheel airplane into a right quartering headwind?

Answer: When taxiing a tailwheel airplane into a right quartering headwind, use up aileron on the right hand wing and up elevator.
My answer: put the control to the right should be enough, why bother the elevator?

The wind could pick up the tail in tailwheel aircraft which is why they recommend elevator up to prevent that scenario.  If the wind is really bad the tail could possibly get higher than the wings and flip the airplane over.  This will not be an issue for tricycle gear aircraft so elevator doesn't matter in this case.  This will be tested on the FAA knowledge exam so you will want to remember this.

It's more to keep the maximum down force on the tail wheel for controlability, and maximum resistance to nosing over when braking.  Same reason you hold the stick in your gut after the tailwheel touches on landing.  My current airplane is tri-gear and I taxi with the stick back to lift the nosewheel at bit higher for prop clearance on gravel.  That can be a problem; I recall an event where a 150 pulled out behind a Dash 7 and went the opposite way with the elevator full up, just as the Dash 7 made a big burst of power on one side to help with a tight turn, and flipped the 150 over.

When taxiing into any headwind component (including a quartering wind) you should use up elevator on most general aviation aircraft.
On a tailwheel aircraft, keeping load firmly on the rear wheel helps provide directional stability and reduces any tendency to pitch forward on braking or when negotiating uneven ground, which in severe cases could risk a prop strike.
On a tricycle aircraft it is less of an issue.  However, there is still some benefit in that it reduces the load on the front wheel/strut.  The pair of rear wheels/struts are usually stronger than the front (as the rear pair are designed to take landing impacts) and so it is preferable to distribute more load to them, particularly on uneven surfaces.

I'd also add that when there's a strong headwind your true airspeed goes up and you start producing lift, that lift transfers weight from the wheels to the wings, holding the elevator back raises the nose up a little putting more weight on the mains, increasing brake effectiveness.


text:
How do electric carbon monoxide detectors work?
How does the electric carbon monoxide detector in cabin or cockpit on aircraft work?

You may find the Wikipedia article on Carbon monoxide detector informative. That article mostly talks about home detectors, but the technology is the same.

Related, "Carbon Monoxide Detectors" on AVweb.

The amount of fire-on-aircraft quesitons you are asking is worrisome :-)

I am currently working on description and operation of fire detention systems for my first shop rotation.

@MyatKhant: Good to know you're not an aspiring arsonist! :-P

There are three major types of carbon monoxide senors.

Biomimetic: A gel changes color when it absorbs carbon
monoxide.
Metal oxide semiconductor: When the chip's circuit detects
carbon monoxide, electrical resistance decreases, and this
triggers an alarm.
Electrochemical: Electrodes immersed in a chemical solution
sense changes in current when they come into contact with carbon
monoxide, and this change triggers the alarm.


text:
Why should a Piper Seneca not take off after an engine failure below 100MPH?
In the Seneca (PA34-200) AFM, in the ENGINE FAILURE DURING TAKEOFF section, it is noted that if engine failures occurs during takeoff ground roll and 100 MPH has not been attained, the pilot must abort the take off and if attained the pilot must continue. Since Vmc is 80 MPH, why was 100 MPH chosen as the cutoff point for go/abort?

ENGINE FAILURE DURING TAKEOFF
  The single engine minimum control speed for this airplane is 80 mph (CAS) under sea level standard conditions.
a. If engine failure occurs during takeoff ground roll and 100 mph (CAS) has not been attained, CLOSE BOTH THROTTLES IMMEDIATELY AND STOP STRAIGHT AHEAD. If inadequate runway remains to stop, then:
  (1) Throttles - CLOSED.
  (2) Brakes - apply maximum braking.
  (3) Master switch - OFF.
  (4) Fuel selectors - OFF.
  (5) Continue straight ahead, turning to avoid obstacles as necessary.
b. If engine failure occurs during take-off ground roll or after lift-off with gear still down and 100 mph (CAS) has been attained:
  (1) If adequate runway remains, CLOSE BOTH THROTTLES IMMEDIATELY, LAND IF AIRBORNE, AND STOP STRAIGHT AHEAD.
  (2) If the runway remaining is inadequate for stopping, the pilot must decide whether to abort the takeoff or to continue. The decision must be based on the pilot's judgement considering loading, density altitude, obstructions, the weather, and the pilot's competence. If the decision is made to continue, then:
  (a) Maintain heading and airspeed.
  (b) Retract landing gear when climb is established.
  (c) Feather inoperative engine (see feathering procedure).

Original image of text.

It's specific to this aircraft. The text has explained for you. If you are faster you might not be able to stop within the runway, then keep flying would be safer, relatively. Whenever there is enough runway to stop, stopping is always safer.

Probably below 100 mph the aircraft is not controllable with one engine giving full thrust because the rudder does not provide enough control authority at those speeds.

@user3528438 He assume that we have enough runway available !

@DeltaLima But VMC is 80 so it means we can control the plane above 80mph . we are assuming that we are in sea level . I found no answer for this on internet yet :(

Please avoid posting text inside images, take your time and copy the text in the body of the question here.

VMC is 80 @AminNajibZadeh, however you need a margin above that for safety, also you need to be able to climb.

VMC assumes both engines are operational and the aircraft is not subject to asymmetric thrust. The rudder may not have enough authority to counteract one engine thrust on the Seneca below 100mph.

That’s probably because 100 kts is considered Vsse for that airplane.

@tj1000 - VMC is the calibrated airspeed at which, when the critical engine is suddenly made inoperative, it is possible to maintain control of the airplane with that engine still inoperative, and thereafter maintain straight flight at the same speed with an angle of bank of not more than 5 degrees. Are you maybe talking about some other VMC?

While you are in the ground roll the aircraft is not flying so even with maximum rudder at or above $V_{MC}$ you may not have enough rudder control to limit the deviation from centreline.

I finally found out an answer which makes more sense to me . By test pilot , vmca masured with a lot of citation and one of them Is 5 degrees angle of bank towards the live engine . So it means that we can't have that 5 degrees because we are still on the ground.
for each 1 degree , our speed decreases 3 knots .So 5 degrees = 15 knots which is equalls to 20mph !
 80+20 = 100 mph !
This was the best answer I have got until now.

Please don't add "thank you" as an answer. Instead, accept the answer that you found most helpful.  - From Review

@mins this adds an answer in addition to the "thanks."

@fooot: Sort of... it is a thank you and a proposal that "Im not sure if this is the exact answer".

Unless one was privy to the certification testing and POH drafting of this aircraft, the exact answer is likely not available.  However there are several factors which come into play.
First Ek = 0.5m(v2) so the relative kinetic energy at 80 will be less than 2/3 of the energy at 100 mph. The distance to stop at 80 will be substantially less than at 100. Terminating the takeoff substantially reduces flight risk on one engine, taking off a at a speed very close to VMC with onset drag from the failed engine, and gear extended.
Accelerating to 100 mph will take substantially longer with one engine, and likely it was determined that the stop distance in this situation is less than the remaining distance to takeoff.
Takeoff close to VMC, with the gear down and the onset drag of the failed engine, impair substantially the ability of the aircraft to achieve 100 mph, and risk is reduced by landing the aircraft. Aircraft handling will also be impaired, due to the low speed (and onset drag). If the distance required to accelerate to 100 mph under those conditions exceeds the distance to stop, then the aborting the takeoff reduces the flight safety risk.
14 CFR 25 aircraft require that the takeoff distance and the accelerate-stop distance be less than the available runway length. The Seneca was certificated under Part 23, so this requirement does not apply, yet the concept remains valid.  Accordingly, a V1 speed is not defined for the Seneca.


text:
Does the Osprey have a "worse" downwash than a helicopter of equal weight?
The Osprey is a tilt-rotor which takes off as a helicopter but flies like a plane. It is known for it's nasty downwash which can knock people off their feet and even wreck helipads.
Its rotors are a compromise: larger than a plane's propeller but smaller than a helicopter's rotor. Its weight must be supported on a smaller swept area (higher disk loading). This means a more concentrated downwash. Is my reasoning correct?
Edit: it seems that my physics reasoning is correct. Sophit's link compares, quantitatively, disk area and disk loading between an Osprey vs helicopter of similar mass.

This might help.

The reference you linked to is highly misleading.  The Osprey did not "demolish" a concrete or asphalt helipad.  It just blew away some thin mats that were sitting in a field.  It was not on the mats and the mats did not have any helipad markings.

You wreak havoc. You wreck helipads.

higher disk loading... means a more concentrated downwash

Correct and this can be demonstrated even using a very simplified approach like the momentum theory by which the airspeed  $w$ under a rotor of area $A$ generating a thrust $T$ is:
$w=2\sqrt{\frac{T}{2 \rho A}}$
Being the thrust equals the weight, a smaller rotor implies a higher speed of the air pushed under it. It also implies a higher power which has to be supplied to the rotor to give that thrust. This is why the disc area for an helicopter is normally chosen to be as big as possible.
As you've also highlighted, the disk area of the MV-22 is a compromise among contrasting requirements and the resulting induced velocity of 80kts under it can be classified as a hurricane. That implies, among other things, that the MV-22 cannot for sure land on some unprepared field; the risk of brownout/whiteout is increased; and the fuselage is better accessed from behind instead from the side where the high induced velocities can make it difficult.
To all these it should also be added that at landing, when the engines are rotated vertically, the hot exhaust impinges on the airfield requiring not only a prepared airfield but also a sturdy surface.

Yes, your reasoning is correct.

Do you have any information about the speed of the downwash, and the speed of the downwash of a helicopter of similar size? That information would be pretty interesting.

Simple, correct, concise and to the point... bravo

@TannerSwett Does the question ask for downwash figures? If you want to know more, please ask a new question. All I did was to answer the question asked by Kevin. My understanding of this site is that people ask questions and others answer them. If that understanding is wrong, please educate me!


text:
What plane was most likely used for this TWA transatlantic flight in 1954?
This is the manifest for my grandaunt (she is #9). She most likely took a train from Paris to Croatia to visit her mother. The family was not wealthy, so this was an extravagant expense for them.
Can the plane type be determined from the flight information? Maybe a Lockheed L-1049.

I wonder if we have any info on how much did such a plane ticket cost in 1954. Interesting document for sure!

@Neinstein - I have looked for ticket costs, no success so far. I am also trying to determine how much her husband made. He was an assistant foreman in a coal mine in SW Pennsylvania.

Isn't there a chance the first digit is actually a 7? Making it N6074C?

@GrzegorzOledzki I don't think so, it looks like a typewriter-style 1 for me: https://imgur.com/a/E2ubH8L


text:
Are there equations to match power required to mass for rotorcraft?
Is there an equation (or table or whatever) to determine what power is required to fly certain mass? Probably there will be a bunch of nuances, but at least some sort of rule of thumb probably exists.

The simplest way is using the momentum theory, by which the thrust $T$ generated by a rotor is:
$ T = k\sqrt[3]{2 \rho A P^2} $
where $A$ is the rotor area, $\rho$ is the density and $P$ the power needed to spin the rotor. This equation is strictly valid only at hover but being the highest thrust normally required in hover, then it's just perfect for your purpose. The $k$ is a coefficient taking into account limitations of the momentum theory and "bunch of other nuances" : a value of $0.5$ can be used in a conservative way.
Obviously $T$ equals weight $ T = W = mg $, where $m$ is the mass and $g$ the gravity.
If you have some numbers in mind we can plug them in and see what we get

Thank you, ill post an excel graph for sanity check

@sophit, The cube root does not render well on my browser.  You might change to $()^{1/3}$ instead.

@RobMcDonald: I've used "\sqrt[3]" which should be the standard way to render the cube root, no idea why it doesn't work properly, thanks anyway for pointing that out

OK, here is what i get. https://pasteboard.co/BRRPEZr0dDNW.png  It's power in megawatts against mass in kg. The steps are due to propellers total area i assumed (50 to 500 m^2). Seems reasonable for 1 ton, but for 20t seems like ten times what i expected. What do you think?

@sophit would you like to consult me for a fee? I don't see private messaging here, if you are willing to talk, I'll post my email here

I'd plot one line per each disk area so to have a clear view without steps. I'd suggest you also to get a copy of the legendary Helicopter Aerodynamics by Raymond W. Prouty. Very easy to read, fluent and almost without equations. Which project do you have in mind actually?

Let's talk offline, please. Email me at lapserdak # gmail * com, i really want to have a consultation with someone who understands the matter

@sophit what time zone are you in?

I got it now, it went to spam. Thank you!

In a hover, the figure of merit $FM$ is defined as the ratio of the ideal power required to the actual power required.
$FM=\frac{P_\mathrm{ideal}}{P}$
Typical values for the figure of merit are about 0.7.
Momentum theory tells us the ideal power required in a hover.  We can combine these to give the hover power required.
$P=\frac{T\sqrt{T/(2\,\rho\,A)}}{FM}$
Where:
$P$ is the hover power required.
$T$ is the thrust.  In hover, thrust equals weight.
$\rho$ is the density of the air.
$A$ is the disk area.
$T/A$ is the disk loading.
More power is required to climb.  More power is required to power the tail rotor to offset the torque of the main rotor.  More power is required to overcome the drag of the fuselage.
Power required for forward flight gets substantially more complex.
There are equations to calculate or estimate all of these things.  That is what aerospace engineers do.  Johnson's Helicopter Theory is probably the most comprehensive and least expensive.  However, it is an intense book -- not for the faint of heart.

This is awesome, thank you very much!

would you be able to consult me? I'd pay for your time

Sorry, I am not able to take on more consulting clients at this time.

Thank you anyway!


text:
What does "Information <letter>" in ATC transmissions mean?
When listening to ATC broadcasting (at least for ULLI), phrase "Information <Charlie|India|whiskey|etc.> on board" may be heard. Charlie, India, Whiskey, etc. refer to "C", "I", "W" but what do these codes mean? What kind of information is this?

Charlie is one of the controllers' boyfriends who lives out of town and can only visit every few weeks; India obviously refers to the nationality of the passengers and whiskey to the contents of the drinks trolley. ;-)

...and Bravo clearly refers to the applause that comment gets for making me chuckle :)

This is a simple versioning system used in ATIS (Automatic Terminal Information Service).
ATIS messages contain information about the weather at the airport, runways in use etc. This information is transmitted on a dedicated radio frequency and repeated in a loop. The ATIS messages are updated frequently as the weather or operations at the airport change. Every time a new ATIS message is generated, the letter is changed.
Example of an ATIS message:

This is Schiphol arrival information Kilo, main landing runway
  18Right. Transition level 50. Two zero zero degrees, one one knots.
  Visibility 10 kilometres. Few 1300 feet, scattered 1800 feet, broken
  2000 feet. Temperature 15, dewpoint 13. QNH 995 hectopascal. No
  significant change. Contact Approach and Arrival callsign only. End of
  information Kilo.

Now when for example the temperature or pressure at the airport changes, the ATIS information is updated:

This is Schiphol arrival information Lima, main landing runway
  18Right. Transition level 50. Two zero zero degrees, one two knots.
  Visibility 10 kilometres. Few 1300 feet, scattered 1800 feet, broken
  2000 feet. Temperature 16, dewpoint 13. QNH 994 hectopascal. No
  significant change. Contact Approach and Arrival callsign only. End of
  information Lima.

The flight crew will listen to the ATIS often before they are in contact with the Air Traffic Control of the airport. They note the information in the ATIS, together with the information version letter.
On first contact with the airport's Air Traffic Control they will state what version of the ATIS they have listened to.

Schiphol approach, this is KLM1234 with information Lima.

The Air Traffic Controller can then determine whether this is the latest version of the ATIS or if there is newer information available that should be passed on to the flight crew.

This was Aviation SE information DeltaLima.

when does it reset?

@DavidRicherby But then I would have to change my username after every edit I make!

@DeltaMike Indeed.

@ratchetfreak It resets at the end of the range. Some airports use the entire A-Z range, others only a subset.

@ratchetfreak FYI Schiphol just went from Lima to Mike and then back to Alfa

@ratchetfreak And Schiphol is now (three and a half hours later) at Lima again.

@ratchetfreak: I vaguely recall they restart at alpha every day (at midnight presumably).

One halloween, just for fun, the local airport was publishing information "Spooky", "Transylvannia", "Undertaker", "Vampire", , etc...    I think the pilots enjoyed that little deviation from the regs. :)

@ratchetfreak I'm not sure if there's a reg for resetting the ATIS letter (at least not in the US - and I've never been at the airport early enough to pick up the first broadcast of the day to see what they do - I like to sleep in!) - It does however cycle back to Alpha when information Zulu expires or is changed.

Information Lima includes: "Contact Approach and Arrival callsign only."  That sounds like the first contact should be "KLM1234" instead of "Schiphol approach, this is KLM1234 with information Lima" (presumably because frequency is usually busy).  Is that right?

@mgkrebbs I think it's mostly to prevent complete status reports ("this is KLM1234 flying direct XXX descending through FL200 to FL120") - that takes time and in some cases is unnecessary (such as when it is standard procedure to hand off aircraft with that clearance or when controllers have been in contact "offline").

@RedGrittyBrick in the US, JO 7110.65 2–9–1 a1: Each alphabet letter phonetic word must be used sequentially, except as authorized in subpara a2, beginning with “Alpha,” ending with “Zulu,” and repeated without regard to the beginning of a new day. Identify the first resumed broadcast message with “Alpha” or the first assigned alphabet letter word in the event of a broadcast interruption of more than 12 hours.

In the US, ATIS info is typically updated hourly - unless something unusual/unpredicted happens that is relevant to approaching or departing aircraft.
In the US, ATIS broadcasts include:

Airport Name.
Information letter (Alpha, Bravo, Charlie...).
Time Hour/Minute in Zulu (GMT) when the observation was made
Winds - direction, speed, and sometimes gusts, variability.
Sky Condition - cloud cover (clear, few, scattered, broken, overcast) and altitude
of the layer(s).
Barometric Pressure - which is used to set the aircraft's onboard altimeter to an accurate
reference for the airport it's approaching/departing).
Other remarks, such as runway/taxiway closures, lighting or navigational aids down, etc.

The letters refer to ATIS information, which stands for Automatic Terminal Information Service. ATIS messages are broadcast on a loop on a separate frequency from approach and tower frequencies and inform pilots of weather conditions, active runways, runway conditions, and other important data. Each time the information changes a new recording is made and the version letter increments.
Pilots listen to this information before contacting the approach/tower frequency so that the controllers don't spend their entire day reciting it over and over again.

In the USA, this is defined in the FAA's Air Traffic Organization Policy, Section 2-9-1. According to that source, ATC must:

(a) Identify each ATIS message by a phonetic letter code word at both
  the beginning and the end of the message. Automated systems will have
  the phonetic letter code automatically appended. Exceptions may be
  made where omissions are required because of special programs or
  equipment.
1. Each alphabet letter phonetic word must be used sequentially, except as authorized in subpara a2, beginning with “Alpha,” ending
  with “Zulu,” and repeated without regard to the beginning of a new
  day. Identify the first resumed broadcast message with “Alpha” or the
  first assigned alphabet letter word in the event of a broadcast
  interruption of more than 12 hours.

ATIS information letters always refer to the time of the information, in ATC we use UTC (universal coordinated time) which is typically the GMT (Greenwich time) for example: Information Alpha refer to time 00:00 and Bravo to 01:00 ...up to Information X-ray at time 23:00 then we use alpha for 00:00.

Could you please specify the location for which this answer applies? It is not true for most of the world

answer is not entirely correct. correlation is not causation. just because weather updates every hour does not mean the atis letters represent the time information. There are times when weather changes so quickly that new atis information needs to be broadcasted in less than an hour. In that case atis letter changes not because the time limit but to indicate that new information is available.

@Kolom: not just weather, but runway configuration, or runway condition codes, or other pertinent NOTAMs which arriving and departing pilots ought to know... there are many reasons why "information Alpha, 0154Z" might change to "information Bravo, 0154Z."

This answer is incorrect. ATIS can update multiple times per hour, and the letters simply advance, without any reference to UTC. Also, when multiple airports are in close proximity, their ATIS identifiers are offset from each other, so if BWI has ATIS "A" then IAD might have "K" and DCA "S".

Also, there are some airports (KDEN is especially notorious for this) that update their ATIS about every 10 minutes sometimes... taxiway PP9 is no longer closed? New ATIS! Now they closed PP8? New ATIS!


text:
What does feathering mean and how does it work technically?
Before I ask "What does Feathering mean when it comes to Jet/Propeller Engines" I have to say what I think I know:
Feathering jet/prop engines mean achieving a sufficient turbine rotation speed at which, the general functionalities such as VFG drives (elec), pumps, etc. could start operation.
I would very much appreciate an explanation with any anomalies.

I think "feathering" means disabling the propeller on a failed engine. If you think it means something else, would you like to quote/reference the paragraph in which you've seen that word used?

Feathering is not engine starting, and also is not used in turbine (excluding turboprop) aircraft. In a piston or turbo prop aircraft, in the event of an engine failure, to decrease drag so you can either glide farther or have better performance on the remaining engine(s), you can set the prop pitch lever so instead of facing at a right angle to drive air backwards and produce thrust, the propeller will instead turn edge-first into the airstream, reducing drag. Not all propeller airplanes have this capability, but it's an added safety feature.
In motorgliders (both light sport aircraft and primary) without retracting blades, the feathering position turns the prop so that the edge faces into the airstream and also locks the propeller so it no longer turns.

Yes glide and performance with a feathered prop is better than one spinning in the air like a kid with a pinwheel. But those are happy side effects due to the significant reduction in drag and adverse yaw caused by a free-spinning prop. Moreover a runaway prop can be deadly. The prop can far exceed its normal RPM limits and come apart! Runaway prop blades have known to stretch due to the centripetal forces.

motorglider LSAs in the glider classification can have feathering props.

Feathering is only possible with variable pitch propellers and means that the blades are turned such that their mid-to-outer section is aligned with airflow and they create minimal air resistance. This is done when the engine is shut down and the propeller should create minimal drag. This means also that all accessories on this engine will not be powered anymore.
Due to the normal twist of a propeller blade, some sections are still not completely aligned with airflow and produce more normal force and drag than they would if all sections could be aligned with airflow at the same time, but in total those forces will cancel out, and the propeller stops windmilling.

This picture of a C-130 engine with feathered prop should help to illustrate the concept.
On pure jets no equivalent setting is possible (we have to wait for variable-pitch fans to add this in the future).

RE: C-130 feathered prop... The feathered position is such that the prop actually wants to turn backwards. This keeps the prop tight against the prop brake to ensure that the thing does not turn.

Feathering means to align the propeller blades such that the pressure difference between the camber face and back face are almost equal and hence they produce no thrust or drag.
This feature is mostly incorporated in Multi Engine TurboProp Aircrafts such that if there is an engine failure (any one of the engine); the propeller blades of that engine are feathered so that they produce the minimum drag and also to prevent the windmilling (a condition where the air flow rotates the propeller and in turn the engine, this is a situation where engine is rotating without lubrication and is a very serious concern).
So, when an engine fails the singe acting propeller blades which are fitted with counterweight, have a tendency to rotate toward the high pitch or coarser pitch (toward feather) which is also assisted by a spring inside the pitch change cylinder. If the propeller is a double acting and without counterweight they are usually provided with Manual Feather Pump which works even if the engine is not running and help turn the propeller blade by oil pressure in the cylinder and helps in minimizing the drag or prevent the windmilling condition.


text:
Can non-instrument rated pilots request practice approaches?
I'm working on my instrument rating and wondering if I can practice ILS approaches without an instructor? Using a safety pilot, also not instrument rated, could I call approach stating VFR would like ILS into X. Or do I just call the tower and ask for it there? Or can I only do this with an instructor?

This would be in the US.

Meh! :D I'll leave my answer until someone produces the FAA-equivalent of my references.

Appreciate the answer SentryRaven. I'd leave your answer no matter what. Useful for others in Germany. Thanks!

I do it all the time, especially at night. When I’m coming back at night I almost always fly the RNAV approach to my airport because I know that it will keep me out of the mountains. As long as approach knows what you are going to do, and you make it clear that you will remain VFR, they are fine with it.

Sure you can! There's nothing wrong with shooting practice approaches if you're not instrument rated (in the US, at least) as long as you don't actually accept an IFR clearance.
You would probably be better off asking approach control for practice approaches rather than tower, if you have approach available to you.

A useful addition might be if you know whether/what difference there is in what you can log.

Yes, you can request practice approaches under VFR, however you or a safety pilot needs to take over airspace monitoring if you put on an IFR hood.
Unless your question is FAA specific, here are some excerpt from the German AIP.

562 VFR-PRACTICE APPROACHES
562.1 A practice approach may be approved for VFR-flights intending to use an
  instrument approach procedure for training purposes.
562.2 When giving heading and altitude recommendations during VFR-practice
  approaches, it shall be explicitly emphasised that it is a suggestion.
562.3 If appropriate, altitude information shall be provided to ensure compliance
  with the minimum safe height.

And also the associated phraseology to request:

A:  REQUEST (type of IFR approach) PRACTICE APPROACH VFR
  G:   (type of IFR approach) PRACTICE APPROACH VFR APPROVED / NOT APPROVED

This is covered in Aeronautical Information Manual (AIM) 4−3−21. Practice Instrument Approaches
and makes several references to 14 CFR part 91 -- mostly for VFR flight.  Here is the important part:

Pilots not on IFR flight plans desiring practice instrument approaches should always state ‘practice’ when making requests to ATC. Controllers will instruct VFR aircraft requesting an instrument approach to maintain VFR. This is to preclude misunderstandings between the pilot and controller as to the status of the aircraft.

For some uncontrolled airports, ATC cannot service practice IFR approaches.
Once cleared for the approach, ATC will assume responsibility for IFR and VFR separation as IFR.  Just as with IFR flight plans, some diligence is required by pilots to avoid pattern traffic at uncontrolled airports.
This section is fairly detailed with 11 subparagraphs. The complete AIM is available from https://www.faa.gov/air_traffic/publications/


text:
If "flight time is compensation", how can a PPL holder legally fly at all?
I have seen a strange phrase "flight time is compensation" in a few questions and answers here, mostly related to what PPL can do for free and what is not allowed.
This looks so confusing that I ask a question. If the private pilot cannot get the compensation, and flight time is a compensation, how could such pilot legally fly? One should theoretically get CPL before having the possibility to log any flight time.
This is surely not the case, I understand. When the "flight time is compensation" and when it probably is not?
Most of the confusing questions are related to USA (so FAA).

Flight time is only considered compensation when the pilot is not paying all the costs associated with the flight.  If the costs are to be shared the following advice is recommended.
A private pilot can be compensated, up to a pro-rata share, of the cost of that specific flight.  This would include rental fees, fuel, oil and such.  It does not include items like insurance and annual inspection fees.
The overall regulation is found in §61.113(b & c).

(b) A private pilot may, for compensation or hire, act as pilot in command of an aircraft in connection with any business or employment if:

(1) The flight is only incidental to that business or employment; and
(2) The aircraft does not carry passengers or property for compensation or hire.

(c) A private pilot may not pay less than the pro rata share of the operating expenses of a flight with passengers, provided the expenses involve only fuel, oil, airport expenditures, or rental fees.

You should be able to see pretty quickly that you are allowed to transport yourself by private airplane to a business meeting.  There is good reason to fly to; depending on the distance, it could be quicker to fly a private airplane than it is to drive saving you time and money.  However, the moment the company decides that you should fly to all of your meetings it is no longer incidental to that business and operations must cease.

If you want to fly passengers, and also want them to pay their pro-rata share.  There are three things that must be considered.

There must be a bona-fide purpose for the PIC to make the flight.  The reason cannot be that the passenger has a business meeting at the destination and you want to get lunch.  You, as the pilot, must have a reason to make the trip, whether or not the passenger(s) come along.
The PIC must dictate where the flight is going to go.  Again, you cannot make a flight with passengers where you drop them off at one airport while you fly to a different airport.  Why would you land at the first airport, if you have no need to land there?
You cannot "hold out" or advertise that you are going somewhere and wait to see if other passengers are interested in going to the same location.  There are websites that have been shut down by the FAA for doing just that.

The Lamb Interpretation
The Mangiamele Interpretation
The Chero Interpretation

December 26, 1985
Thomas H. Chero
  Vice President - Legal
  AVEMCO Insurance Company
  Frederick Municipal Airport
  411 Aviation Way
  Frederick, MD 21701
Dear Mr. Chero:
Thank you for your letters to this office, dated September 9, 1985, and October 23, 1985, respectively, concerning the actions of the Pilots and Passengers Association (PPA).
You are correct in stating that Section 61.118 of the Federal Aviation Regulations (FAR) prohibits private pilots from participating in PPA's operations. Section 61.118 provides that a private pilot cannot act as pilot in command of an aircraft that is carrying passengers for compensation or hire unless the flight falls within one of the four listed exceptions in 61.118(a) - (d).
Section 61.118(b) allows a private pilot to share the operating expenses of a flight with his or her passengers. Additionally, the FAA has interpreted 61.118(b) so that the only allowable share-the-costs operations are those which are bona fide, that is, joint ventures for a common purpose with the expenses being defrayed by all passengers and the pilot. Nor does Section 61.118 permit pilots who want to build up time toward their commercial pilot certificates to carry expense sharing passengers to a destination at which they have no particular business. (emphasis added)
PPA pilots apparently would not share in the expenses of the flights they would undertake. It also appears that PPA pilots could be flying to destinations at which they had no particular business. The PPA system is not a casual one of an individual pilot wishing to take some friends or acquaintances with him on a trip. The PPA system would violate the letter, as well as the spirit, of Section 61.118.
Even if the pilot bears an equal share of the expenses with his or her passengers and indeed has his or her own need to fly to a particular destination, yet another problem arises. Since PPA's passengers would be solicited for flights by PPA from a broad segment of the general public, we conclude that each pilot carrying paying passengers from PPA would probably be engaged in common carriage. This means that each pilot would become an air carrier subject to the certification and operating rules of Part 135 of the FAR.
We appreciate your calling our attention to this matter.
Sincerely,
John H. Cassady
  Assistant Chief Counsel
  Regulations and Enforcement Division

But if the pilot practices every day from early to late near the same airport, are these flights "incidental" or something else applies here?

@h22 The "something else" that applies is some simple financial logic: You can't really compensate yourself (unless you're part of a sophisticated counterfeiting operation) - we usually call compensating yourself "spending your own hard-earned money". When nothing else in FAR 61.113 applies to allow you to accept some form of compensation (money, lunch, goats, favors owed, free flight time, etc.) you are solely responsible for the expenses of the flight, so as long as you pay the full cost of those practice flights you're OK.

The phrase "flight time is a compensation" doesn't mean that flight time is always necessarily compensation. For example, if someone said "A policeman cannot receive compensation other than their salary. Meals are compensation." that doesn't mean policemen can't eat, it means they can't accept free food.

@voretaq7 Well there goes my idea for bleet.aero, a flights-for-goats website.

@ZachLipton Elevator pitch unclear: Placed goat in captain's chair.

So, does paragraph b mean that your employer can pay the fuel/rental expenses and pay you for your time to fly yourself to a meeting?

Thank you for this answer. There is another question on this site where people argue that flight time is always compensation, and it would be good if you were to correct them.

@DJClayworth The FAA does seem to consider ALL logged flight time as compensation  if the pilot pays nothing. in its 1997 Harrington Legal Interpretation While it could be argued that the accumulation of flight time is not always of value to the pilot involved, the FAA does not consider it appropriate to enter into a case-by-case analysis to determine whether the logging of time is of value to a particular pilot, or what the pilot's motives or intentions are on each flight.

What if the company doesn't ask the pilot to fly to meetings; (s)he just chooses to fly to every meeting?

Because the PPL pilot is typically paying the costs to fly, and doing so for their own purpose. It becomes illegal (compensation) when someone offers to a private pilot to fly for below prorated cost for some other purpose, commercial or otherwise.

"below prorated cost"... Flying passengers can be illegal even when the cost is shared evenly.


text:
What twinjet with rear-mounted engines and swept wings did I see in Savannah, GA?

I saw this flying in Savannah, GA and need help identifying it. It looks like something military due to the color and lack of markings. Can anyone help?

Hi Annette. I edited the title of your question in an attempt to briefly describe the airplane you saw. Feel free to [Edit] further.

It looks like we have not yet decided between 500 and 600 !

Gulfstream G500. The G600 is longer. The angle is close, but look at the window just ahead of the wing fairing. The original is faint but clearly ahead of the fairing curve. The G600 window is in the middle of the curve. The G600 has a bigger wing.

G500 pinterest

G600 wikipedia

Is that the G600 Lancer variant? On its way to a jousting competition?

Refueling probe :)

Flying narwal??

Airspeed probe.

"See, this is how you thread the Space Needle..."

It looks like a green Gulfstream G-650, which makes sense since Savannah is where they are made.  "Green" means unpainted (just in epoxy primer or bare metal in spots) and with no interior.  That's how corporate airplanes usually leave the factory.  Finish paint and interiors are normally custom done at completion centers selected by the purchaser.   There is a completion center across the ramp from Gulfstream, Midcoast Aviation, that probably does some of them, although as I said that's the buyer's choice.
Corporate manufacturers usually leave the completions to outside companies because the artisan level of work required doesn't dovetail well with normal production processes.  You have to have an interior with pretty much perfect joins and seams or the customer will reject it.  Bombardier starting doing Global completions in house and it was a disaster for quite a while, with customers forcing complete interior re-dos.

It’s a G600 test article (slightly longer fuselage than a G500) undergoing a test flight in the airspace near Hilton Head Intl (KSAV) where Gulfstream’s main factory and flight test center are.  They often fly them south from KSAV to Brunswick (KBQK) for flight testing.  The aircraft is not yet certified for production, nor is the G500 either.

That's a Gulfstream G500 or G600 (someone who knows the differences better can tell us which), probably a new one arriving to Hilton Head International for finishing at the Gulfstream service center there.  It doesn't have its final paint job yet, hence the lack of markings.

https://en.wikipedia.org/wiki/Gulfstream_G500/G600#Specifications This lists the differences.


text:
How do you open and get a IFR clearance while in the air?
I once had a traffic controller give me a hard time about how I requested IFR clearance once in the air. I had previously filed an IFR flight plan, and took off from my untowered home airport. On approach control's frequency, I said:

Tampa Approach, Cirrus 123AB, 5 miles southeast of Tampa Exec at 1000 feet, IFR to Ft. Lauderdale Exec

The approach controller responded, annoyed, saying something like "Well do you have an IFR flight plan or are you reporting IFR??"
I had always used that phraseology because it seems the least wordy way to get the info across, which can be helpful when the freq is busy. What is the technically correct way to get an IFR clearance on an existing IFR flight plan?

Looks like you generally omit a key word, request". Just make it request IFR to FXE.

There is one example in the AIM used for transitioning from VFR to IFR, and it how I've always done it:

AIM 5-2-5. Abbreviated IFR Departure Clearance (Cleared … as Filed) Procedures
EXAMPLE-
  "Los Angeles center, Apache Six One Papa, VFR estimating Paso Robles VOR at three two, one thousand five hundred,
  request IFR to Bakersfield."

Reference: 5−2−5. Abbreviated IFR Departure Clearance (Cleared … as Filed) Procedures (13 MB PDF)
Notice that they specifically say "VFR" right before their current location and also use the word "request" to make it clear what they are looking for.  I would change your request to:

Tampa Approach, Cirrus 123AB, VFR 5 miles southeast of Tampa Exec
  at 1000 feet, request IFR to Ft. Lauderdale Exec

You might want to make it clear that you have an IFR flight plan on file - e.g. "..., request IFR as filed to " or "..., IFR request, on file, to "

@sdtom You can do that if you like, but it would be non-standard.  This is right from the AIM. :)

For the last part, i've always said "...Would like to pick up our clearance to Ft Lauderdale Exec" so he knows the flight plan is already filed and this is not a pop-up request.

also, the "VFR" portion is to reduce controller workload, so he not wondering where the hell did this airplane come from and why doesnt he have it on his screen and where is the ticket

To add to the above (especially @rbp), the controller should have a proposed IFR departure strip in front of them and should know this isn't just a pop-up air-file request, but the strip may have gotten lost, or may not have been delivered to them yet, or if you're early and it's more than 30 minutes before the proposed departure time it won't have printed out yet.


text:
Why are there speed restrictions applied after deicing an aircraft?
The information about the 737 here mentions an interesting limitation:

737-6/900 without stiffened elevator tabs:
After any ground deicing/anti-icing of the horizontal stabilizer using Type II or Type IV fluids, airspeed must be limited to 270 KIAS until the crew has been informed that applicable maintenance procedures have been accomplished that would allow exceedance of 270 KIAS. Once the applicable maintenance procedures have been accomplished, exceeding 270 KIAS is permissible only until the next application of Type II or Type IV deicing/anti-icing fluids.

How are certain deicing fluids, un-stiffened elevator tabs, and airspeed related here?

Some deicing fluids can leave a gel-like residue on the airplane. Several incidents occurred with 737s where the residue accumulated in the elevator balance bay, causing severe oscillation/vibration in flight above 270 KIAS. These incidents resulted in the issuance of Airworthiness Directive (AD) 2002-08-20, which required adding the 270 KIAS limitation you discovered into the 737's Airplane Flight Manual (AFM). The required "maintenance procedures" consist of cleaning off the deicing fluid residue. The AD also requires a one-time cleaning and sealing of the elevator balance bay.

The FAA has received reports of numerous incidents of
  severe airframe vibration, or limit cycle oscillation (LCO), in flight after the horizontal stabilizer had
  been deiced/anti-iced on the ground. The reported incidents occurred on Boeing Model 737-600, -700, and -800 series airplanes. The empennage structure on these, as well as Model 737-700C series
  airplanes, is identical; therefore, all of these airplanes are subject to the identified unsafe condition.
  These events have been attributed to an accumulation of deicing/anti-icing fluid or other residue in
  the elevator balance panel cavities and on the external surfaces of the elevator tab.

A Boeing article on the subject gives some more information and also has some photos showing the residue. Here's what a gummed-up 737 elevator balance panel looks like:

From the article:

Airplane deicing and anti-icing fluids can leave residue in critical areas in the wings and stabilizers. This residue can rehydrate and expand into a gel-like material that can freeze during flight and cause restrictions in the flight control systems. Therefore, attention to this residue should be part of a regularly scheduled inspection and cleaning process.

...

Although Type III fluids have not been specifically linked to any events involving flight controls, the composition of these fluids makes them equally susceptible to residue problems as the Type II and Type IV fluids.


text:
When and why is the SELCAL (Selective Calling Radio System) check being performed?
When and in what scenario is the SELCAL (Selective Calling Radio System)  check being performed by crew?

If you are unsure whether your SELCAL equipment is properly working, you can request a SELCAL check on a HF-enabled radio frequency. The ATC unit will send out your SELCAL code for testing purposes.

I'm not sure my selcal unit is working, is there anywhere I can test it?
Yes, several places.  If you are located in:

Europe or east of 30W on the North Atlantic, call Stockholm Radio
Eastern USA/Canada or west of 30W on the North Atlantic, call New York ARINC
Western USA/Canada or Pacific, call San Francisco ARINC
Asia - daylight hours, call Singapore or Manila Radio on 8942 KHz USB

[...] All selcal checks are free of charge - just call the station with the aircraft registration mark and when you receive a reply ask for a selcal check and give your selcal code.  The operator will send out your selcal tone and - assuming the selcal unit is working - you will hear a chime in the cockpit.  Acknowledge by replying 'selcal check okay' and you're done!   If your selcal check doesn't work the first time it is worthwhile asking for a 'double' which means you get 2 sets of tones sent out back-to-back and often cures any issues.
(Source: www.selcalweb.co.uk)

Shannon will also give you a SELCAL check.


text:
What careers are available for someone with a PPL?
I'm not sure if this is the right place to ask this question, and I'm sure that some of the answers will depend on the country, so I apologise if this is "too local" or "off topic".
I'm considering getting a Private Pilot's License. Ideally it will be for both recreational use and also to make money.
I've read that there are some limitations on how you can make money as a Pilot with only a PPL. But some of the things I've read a pretty vague and open to interpretation.
What kind of jobs/careers can you get with a PPL?

You cannot be paid if you've just a PPL. You need a CPL to be compensated. For a CPL, you need Instrument Rating too, otherwise you can only fly as VFR.

"Private pilots license" and "to make money" are incompatible.

@Farhan - Australia; As of Sept 1, no longer required to hold an Instrument rating, as Junior Grade 3's can no longer do BIF or NVFR Training.

@merge delete - In future, if you could specify which country you are looking at as part of your question, this will help narrow down the answer to the appropriate law. :)

I would have but when I do that on other SE sites, the bloody yanks mark it as "too localised" and close it.

@mergedelete - on this SE, it's required.. otherwise every thread with EASA or FAA tagged in it would be closed. The difference with this SE is we are talking about variations in law depending on Country.

For Australia, you are extremely confined as to what you can do with a PPL to earn money. Skywriting as people have mentioned, will probably mean you lose your license here. What you can do according to CAR 2.7 (Civil Aviation Regulation) is essentially;

Crop Dusting on a person's property using their aircraft (only on their property)
(You would also require an Agricultural Rating for this)
Transporting the owner of the aircraft

Now, here's where you can work within the rules. According to the definition of the CAR, you can logically fly charter flights as private if you are transporting the owner of the aircraft. What if the aircraft is owned by a company? Logically, anyone who works for that company is considered an owner, or goods reasonable similar to property of the owner.
Now, take everything I've said here, take with a grain of salt as I am not a CASA lawyer (Thank god), and as a disclaimer, nothing that I have said here can be taken as an exact interpretation of the law or anything reasonably similar.
But, have a read of that CAR, and you will possibly find avenues to follow, or just bite the bullet, go to a VET Fee Help approved school and do your CPL?

Thanks for your answer James. WTH??? YOU CAN GET FEE HELP? IM SO DOWN! (but I need to sleep first)

Yep, sure can.. I did mine at Hunter Valley Aviation in Cessnock (part of Basair) under VET Fee Help.

just because you can transport the owner of an aircraft doesn't mean you can get paid for doing so... More likely you're allowed to fly aircraft owned by a company with company staff as passengers, as long as you're not being paid for doing so.

@jwenting - by Australian law, you can get paid to fly the owner and/or property considered as such, as long as the conditions fall within CAR 2.7.

If you are talking about Europe (EASA) Doc 1178 states at PPL privileges:

a) The privileges of the holder of a PPL(A) are to act without remuneration as PIC or co-pilot on aeroplanes or TMGs engaged in non-commercial operations.
(b) Notwithstanding the paragraph above, the holder of a PPL(A) with instructor or examiner privileges may receive remuneration for:
(1) the provision of flight instruction for the LAPL(A) or PPL(A);
(2) the conduct of skill tests and proficiency checks for these licences;
(3) the training, testing and checking for the ratings or certificates attached to this licence.

Bottom line you could make money with PPL by being a flight instructor or a flight examiner. A side effect would be also accumulation of flight hours that would permit you to continue with a course for commercial pilot.

thanks for the answer. That sounds very similar to what I've read for Australia (where I live), too. You know those guys that write words in the sky with the smoke? Can you charge for that with just a PPL?

@mergedelete That's called Skywriting.

@mergedelete: I never thought about it. Probably it is considered aerial work (the same category with agriculture flight, firefighting, etc), operations that you cannot perform with PPL. But, again, I'm not 100% sure about this.

The EASA PPL also allows a PPL to be reimbursed for flying expenses provided that the flying is not necessary for the job. So if someone had an job that requires travel and the company paid flying expenses as part of that travel there's no issue.

@GdD That's interesting to note because that is specifically NOT allowed for FAA private pilots. Other passengers may split the cost of flying the aircraft with the pilot, but the pilot must personally pay at least his share of the costs, IIRC.

For the U.S., career options for someone with a private pilot certificate can be summed up as "stuff that doesn't involve flying an aircraft." It is illegal to be paid for your services as a pilot in the U.S. without a commercial pilot certificate. The flight instruction exemption mentioned above for Europe does not apply in the U.S. All CFIs in the U.S. are required to have a Commercial Pilot Certificate first. Also, for airplanes or other powered-lift aircraft, the CFI must also have an instrument rating in the U.S.
One exception to note is that private pilots in the U.S. may operate an aircraft for the furtherance of a business provided that they are not being paid for flying the aircraft. So, you could, for instance, fly yourself on a business trip if you have a PPL.
Source for CFI requirements: 14 CFR 61.183


text:
How are there some Victor airways that exceed the service area of the VORs they are identified by?
As you can see here, V267 has a length of 149nm, is defined by the Craig VOR (CRG) and the Dublin VOR (DBN) and has a MEA of 3000. According to the AIM, the Service volumes of VORs never reach more then 40nm underneath 14,500ft.
Yes, the Craig VOR or rather VORTAC is described to have the Standart High Altitude Service Volume in the A/FD, but at the MEA, which should also guarantee reception of the navaids in use, the range is still only 40nm. A route at that altitude between those two navaids should only be <80nm, so how can it be 149nm?

It says it right there on the page where the service volumes are described in the AIM:

1-1-8. Navigational Aid (NAVAID) Service Volumes
c. Standard Service Volume limitations do not apply to published IFR
  routes or procedures.

So V267 has been flown at the MEA by an FAA plane, and it obviously met the signal accuracy requirements to be usable at the distances charted.

So that implies that the Service Volumes are just areas of guaranteed coverage while you might be still able to receive a signal out of them?

@Maverick283 Correct, the signal is normally usable further out than the guaranteed service volume, but as you might imagine, it is not guaranteed.

and the limitations are real. These are for DBN:
HIWAS BROADCAST. VOR PORTION UNUSABLE 215-285 BYD 10NM BLO 3,500 FT. VOR PORTION UNUSABLE 001-139 BYD 33 NM ALL ALT. VOR PORTION UNUSABLE 001-139 BLO 5,000 FT AL DIST.


text:
Is there anything a copilot can do to stop a pilot from doing anything while flying?
Is there anything a copilot in a commercial aircraft can do to stop a pilot from doing anything while flying?
As I see it, there are two scenarios:

The pilot is going to do something malicious, in which case the copilot could physically try to restrain or disable the pilot.
It's not malicious, but just something that is a bad idea (say could get the pilot fired or in legal trouble). In my imagination, this could be something like a dangerous like a fly-by.

This question is a different from this one, since the scenario in that question is when the pilots are cooperating but have some misunderstanding on when command is transferred to one from the other, or if one doesn't accept to receive command of the aircraft.

@Pondlife That question is different

You mean something other than physically assaulting them? Like are you asking if there is a "disable pilot controls" switch?

That's why it's only a "possible" duplicate :-) But you may get a better answer if you make it clear why it doesn't help you.

@Pondlife Updated!

Not exactly the same question, but the answer applies directly: https://aviation.stackexchange.com/questions/40777/does-pilot-monitoring-have-authority-to-go-around-in-exceptional-circumstances/40779#40779

Just a sidenote, there is no such thing as "pilot" and "copilot". All pilots in the cockpit are equally qualified and either can be the one flying the aircraft.

@J.Hougaard, really "copilot" is just a more common term for First Officer, and the FO, (while qualified and capable) is generally less qualified than the Captain.

@MichaelHall Less experience and lower rank within the airline, sure. I'm not sure I would say less qualified

We are probably splitting hairs here, but a FO is not qualified to be a Captain!  ;)


text:
What do the various A340 configurations (clean, 1, 1+F, etc.) mean?
Could anyone describe (or direct to usable documentation) me aircraft configurations? What does it mean clean configuration, configuration 1, 1+F, 2, etc... Is there any section in FCOM's describing it in clear way?

You don't have to sign your question like an email. We got a link to your user right there at the bottom right ;)

@zundi - it's a hard thing to get used to...

A clean configuration is a configuration where landing gear, flaps, slats, spoilers etc. are retracted.
1, 1+F, 2, 3 and FULL refer to the level at which the flaps are currently deployed:

Thanks for clear answer, it helps a lot! Could you clarify, is it taken from fcom (exact chapter) or some other documentation?

The image comes from the FCOM Aircraft Systems, 27 Flight Controls, 30 Flaps & Slats, 20 Controls & Indications, - Pedestal (source: http://www.pprune.org/tech-log/520309-clarification-a320-qrh-flaps-slat-failure.html)

Do you remember whether the 1+F position is selected during extension or retraction?